Fasteners, particularly screw type fasteners drive through and/or into two objects, securing them to one another. In certain applications, it is sometimes necessary to use fasteners with counter-sunk heads for clearances or aesthetics. Typically, holes for such fasteners need to have a countersunk opening drilled to accommodate the countersunk head, and various countersinking tools are known to separately countersinking the opening or to simultaneously countersink the opening as the hole is drilled. One issue here is that an extra countersinking step is required to install otherwise self-drilling screws.
Fasteners with a countersunk head that include a radially extending cutting edge that extends to the circumferential edge of the screw head to countersink the surface as the screw is installed are also known. These may be used successfully in certain applications, such as in wood or laminate surfaces; however, attempting to use such self-countersinking heads in a sheet metal surface or a sandwich panel with a sheet metal skin has not proven successful due to the creation of burrs that are not only sharp and dangerous, but may compromise the integrity of the screw attachment and the sheet metal itself. Additionally, there can be overcutting of the countersink, resulting in a knife edge of the sheet metal acting on the shaft rather than a more desired cylindrical portion of the hole. Finally, the cutting edge can severally mar the panel surface at the periphery of the head.
It would be desirable to provide a self-drilling, self-countersinking screw that addresses the issues noted above.